Relay circuit for machine control



Feb. 4, 1941. I J. w. MILLS RELAY CIRCUIT FOR MACHINE CONTROL Filed June13, 1959 INVENTOR.

JOHN W. MILLS Patented Feb. 4, 1941 UNITED STATES PATENT OFFICEApplication June 13,

Claims.

This invention relates to relay electric circuits for general machinecontrol and particularly for controlling various machine movements bythe work passing through or positioned in the machine in the course ofmanufacture.

The principal object of the invention is to provide a relay circuit ofthe kind mentioned which may be easily adgiusted to any desiredsensitivity, will operate without requiring the moving of electriccontacts, and provides for operation of the relay element only upon theclosing of any predetermined number of contacts. Other features andadvantages of the circuit will appear in the following description andaccompanying drawing.

In the drawing:

Figure l is a diagrammatic representation of an electric circuit formachine control incorporating the features of my invention.

Figure 2 is a diagram showing how movable electric contacts foractuation by the work may be used in the circuit in place of fixedcontacts. Figure 3 shows a modified form of the invention.

Before describing my improved machine controlling relay circuit, it maybe said that in the operation of various industrial machines such aspunch presses and metal slitting and cutting machines, it is commonpractice to have some automatic device which must be contacted by themetal or other material worked upon when in a certain position beforethe press or machine can be tripped to punch or cut the metal. Suchdevices aregenerally mechanical latches, trips, or triggers, which inturn release other parts and permit the machine to function only afterthe piece of metal has been properly inserted in position against thesedevices.

In automatic machinery such as can making machinery where sheets of tinare fed into machines at great speed there are commonly provided specialelectric contacts which are closed by the striking of the edge or sideof the tin sheets and which control the further operations of themachines, so that if a sheet of tin does not arrive at the right placeat the right time, or the sheet of tin is deformed such as by having itsedge bent over so that it does not strike the prop er control contact,the machine will stop working or the machine may throw off the deformedpiece of tin, all depending on what the nature of the mechanism is thatis started or stopped by the inability of the sheet of tin to close theparticular contacts or to touch the particular levers or triggers whichcontrol the action.

Generally such devices as above outlined re- 1939, Serial No. 278,909

quire the actual bumping and moving of some small trigger, or flexibleelectric contact, such as pushing one spring electric terminal againstanother to make a contact, and Where electriccontacts are used theygenerally close a circuit which carries sufiicient current to directlyoperate some vital feature of the mechanism. Sometimes such electriccontacts are run on a lower voltage and they operate an electric relaywhich in turn switches in a heavier current to operate a more ponderouspart of the mechanism which the lower voltage current could not operate.Such relays, however, bring in a slower response to the final mechanism,on account of the fact that they involve the magnetization of armaturesand the moving of mechanical parts. Electronic relays have been used forcontrolling various mechanical functions and it is with improvements inthe latter type that applicants invention is directly concerned, thougha modified form of the circuit without the tube also has value.

Applicants arrangement as shown on the drawing uses a thermionic, orelectron tube A as a sensitive relay. This is accomplished by applying anegative bias to the controlling grid so that normally no plate currentwill flow, then upon the metal object or sheet B being placed in themachine C to be operated upon closing a plurality of electric contactsD, E, F forming several resistance controlled legs from the tube gridcircuit and grounding them simultaneously through the machine frame itbleeds off the negative bias from the grid so that the tube will fireand. the operating current will at once pass through the plate circuitand operate the machine.

In the diagram the source of current or house wires are indicated at l,2, of say 220 v. A. 0., connected to the primary 3 of step-downtransformer G with a suitable tap 4 on the secondary for the filament ofthe tube, say 2 v., about a 12 v. tap 5 for the grid control circuit, H,I2, and about a v. tap E for the plate or operating circuit 1, 8.

The operating circuit is preferably fused at H and operates a solenoidor other suitable magnet J which may directly operate, release or lockthe part of the machine K as may be desired, or it may close another orheavier independent circuit Q. Hi carrying electric energy of any typereceived from any desired source, for operating a heavier magnet orrelay L in turn connected to a machine element M.

The grid circuit includes a condenser N, grid leak resistor P, apotentiometer Q, a lead l3 from the potentiometer for adjusting the gridbias, and a ground R, from an intermediate point in the secondary of thetransformer, while extending from lead I3 is a branch l4 separated intothree legs l5, I6, I! which respectively connect to the contact pointsF, E, D on the machine C, and interposed in each leg is a resistor S, T,U. The frame of the machine C is grounded at V so that the metal sheet Bin position on the machine is likewise grounded, and will ground any orall of the contacts F, E, Dupon being placed in position to touch them.

In the diagram a four element electron tube is shown, (G. E. Co.Thyratron FG 98 was actually used), with the controlling grid at W, andan extra grid at X which causes a greater flow in the plate current. Butan ordinary three element tube will operate satisfactorily, eithervacuum or gas filled type.

As the operation of the circuits depends on the relative electricalvalue of the various elements, suitable values for resistor P would be25 m. ohms, resistors S, T and U each m. ohms, and the potentiometer Q,m. ohms and condenser N .l microfarad.

In the illustration it is assumed that the device B is a metal sheet,plate, or other article constituting the work to be operated on in 1machine C, and that before the particular operation the work B must bein precise position to touch all three of the stationary contacts F, E,D (which are in insulated relation to the machine), before the machine,say a punch press, is operated. Under such conditions the potentiometeris adjusted to give a negative bias to the grid W of such a value thatit will take the combined current capacity of all three resistors S, Tand U, to reduce it to a point where the tube will operate when they areconcurrently grounded by properly positioning the work B against thethree contacts F, E, D, and which will at once cause the tube to fireand the plate current to operate the solenoid J (or L if used) and thedesired machine part K or M, as the case may be.

The moment the work B is removed or moved away from the exact position,the grid bias is at once reestablished for repetition with succeedingpieces of work.

It is of course evident that connection [4 may be split into any numberof legs each with its work contact on the machine instead of three asshown, each leg in series with a suitable resistor so that the combineddrain or leakage of all of them will be required to overcome the gridbias to fire the tube, or one contact only may be used if thepotentiometer is adjusted accordingly so that the grounding of but onecontact by the work will fire the tube.

With regard to Figure 1, the work contacts F, E, D are presumed to bestationary after once being set, though they may of course be adjustablefor initial setting, but when the circuit is used for gaging Wor in themachine which is not a conductor of electricity, then instead ofstationary contacts, movable contacts set to close limits may be used asindicated in Figure 2 of the drawing and wherein the contact points F,E, D are each. carried on spring arms I8, I9, 28 secured to the groundedbed or frame C of the machine, and which close against the stationarycontacts F, E, D, of circuit legs [5, l6, 11. It is evident that suchmovable contacts will not gage the position of the work as accurately asthe stationary contacts, also that any number may be used by suitablyadjusting the potentiometer and providing resistors on the circuit legsto correspond so that it will require the concurrent grounding of all ofthem to enable the plate current to flow.

Figure 3 shows a modified form of machine control circuit withoutelectron tube, but using my feature of a plurality of contact circuitlegs each with a resistor S, T, U, in series with it so that the sumtotal of the current flowing through all of them is required to overcomethe resistance of and operate the solenoid or magnet, though preferablyan adjustable resistance Y is interposed in the circuit to permit ofproper adjustment for any number of contacts desired to be used.

In the figure the parts of the circuit corresponding to those alreadydescribed for Figure l are similarly numbered and lettered so thatrepetition of the description is not necessary. In this showing abattery W is shown as the source of current and which may be strongenough to directly operate a magnet or solenoid J of a size capable ofmoving the machine element K desired, or J may be a relay toclose astill higher volt circuit 9, In to operate solenoid L and machineelement M as shown in Figure 1 at corresponding designations.

A study of Figure 3 will show that any number of contact legs may beused, and while I show a grounded circuit, this may be a wired re turn.Also the form of contacts shown in Figure 2 may be employed.

While I have shown grounded machine or work contacts, it is evident thattwo point control or return wire may be used where grounding is notdesired.

If desired to maintain continuous firing of the tube after making acontact on the machine, but one: contact only should be used and thepotentiometer carefully adjusted to establish a very low negative biasso that once the tube is fired the electronic stream to the plate willcontinue until the grid bias is raised definitely beyond the criticalpoint to stop it, or the plate circuit is broken.

One of the particular features of my improved control circuit is thatthe control may be dependent on the work being in precise position atseveral points at the same time before the next machine operation cantake place. Another feature is its adjustment for extreme sensitivity,also the fact that a very low voltage is used on the machine and almostnegligible current flow. Still another advantage is tlrat the rectifyingaction of the tube will yield a pulsating direct current in the plate oroperating circuit for better operating the magnets or solenoids.

From the preceding description and diagrams it will be apparent to thoseskilled in the art that variations in the hook up may be made wluleretaining the important features of the invention, and any suchmodifications are intended to be included in my appended claims.

I claim:

1. An electric control system comprising a thermionic tube having afilament, plate and grid, circuit means for supplying current foroperating said tube, means operated by the plate circuit for controllinga desired mechanism, means normally biasing the grid of said tube to apoint to prevent flow of an operative plate current, and a circuit forovercoming the grid bias provided with'a plurality of paths each withcontacts arranged to require their concurrent operation to overcome saidbias and permit instant operation of said plate circuit.

2. An electric control system comprising a thermionic tube having afilament, plate and grid, circuit means for supplying current foroperating said tube, means operated by the plate circuit for controllinga desired mechanism, a potentiometer for biasing the grid of said tubeto a point to prevent an operative plate current, and a circuit forovercoming the grid bias provided With a plurality of normally openpaths each path respectively incorporating a resistance element of suchvalue as to require the concurrent flow of current through all of thepaths to overcome said bias, and individual contact circuit closingmeans for each of said paths adapted to be simultaneously operated by anextraneous article for concurrently closing the circuit through saidpaths.

3. A machine control system comprising an electric circuit split into aplurality of paths each extending to the machine to be controlled, re-

sistors, one respectively in series with each of said paths, acontrolling element for said machine, means including a single workarticle being worked on in the machine arranged when in a certainposition only to close the circuit through all of said pathsconcurrently, and means operable by the combined current fiowingconcurrently through all of said paths only arranged for operating saidcontrolling element.

4. A machine control system comprising an electric circuit split into aplurality of paths each extending to the machine to be controlled,resistors, one respectively in series with each of said paths, avariable resistance in said circuit, a controlling element for saidmachine, means including a single work article being Worked on in themachine arranged when in a certain position only to close the circuitthrough all of said paths concurrently, and means operable by thecombined current flowing concurrently through all of said paths onlyarranged for operating said controlling element.

5. An electric control system comprising an electron tube having a platecircuit arranged to operate a desired device and a controlling grid, apotentiometer in circuit with said grid adapted for adjustably biasingthe grid to normally prevent flow of an operative plate current, agrounded circuit for overcoming the grid bias to permit instant flow ofplate current provided with at least three paths each having a contactgap spacedly positioned at a remote point and arranged for concurrentlygrounding by an extraneous member when in a predetermined definiteposition, said grounded circuit requiring the combined flow of currentthrough all of said paths to overcome said bias.

JOHN W. MILLS.

